> The one alternative is to distinguish between the two forms of GBK,
> supporting two forms of conversions - one to cp936 and the other to
> "pure" GBK.

Since the idea of "pure" GBK has come up, it should be noted that CP936
(and probably other "GBK-capable" products) do not implement the entirety
of GBK, such as the codepoints that have no non-PUA mapping to Unicode.